Heat treatment apparatus

ABSTRACT

The present invention provides a heat treatment apparatus for carrying out heat treatment for a circular workpiece. The heat treatment apparatus includes a treatment room configured to carry out a predetermined treatment for the workpiece, a transportation mechanism configured to transport the workpiece into the treatment room and out of the treatment room, and a mounting table on which the workpiece transported into the treatment room is mounted. The transportation mechanism is provided with a transportation arm which mounts and transports the workpiece. The transportation arm is provided with at least three transport support pins which support the workpiece when the workpiece is transported, and the mounting table is provided with at least three mounting table support pins which support the workpiece.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat treatment apparatus for carryingout carburizing and quenching treatment for a workpiece.

2. Description of the Related Art

Generally, to improve wear resistance of a low alloy steel or the like(hereinafter referred to as “workpiece”), carburizing treatment andquenching treatment are carried out to allow the surface layer of theworkpiece to interstitially absorb carbon.

An example of a conventional carburizing and quenching treatmentapparatus includes such carburizing and quenching treatment apparatusesdisclosed in Japanese Patent Application Laid-Open No. H10-53809,Japanese Patent Application Laid-Open No. 2010-266176, Japanese PatentApplication Laid-Open No. 2003-183728, and Japanese Patent ApplicationLaid-Open No. H8-285462. As for carburizing and quenching treatmentapparatuses described in Japanese Patent Application Laid-Open No.H10-53809, Japanese Patent Application Laid-Open No. 2010-266176, andJapanese Patent Application Laid-Open No. 2003-183728, a workpiece ismounted on a transportation fork and transported. When carburizing andquenching treatment is carried out in anonline-machining-production-system described in Japanese PatentApplication Laid-Open No. H10-53809, one or more workpieces are treatedby a treatment unit as required in each treatment means. Apparatusesdescribed in Japanese Patent Application Laid-Open No. 2010-266176,Japanese Patent Application Laid-Open No. 2003-183728, and JapanesePatent Application Laid-Open No. H8-285462 are a vacuum carburizing andquenching apparatus in which a plurality of workpieces stacked on a trayis treated. Further, in a carburizing and quenching treatment apparatusdescribed in Japanese Patent Application Laid-Open No. H8-285462, aworkpiece is transported to a desired treatment room by pushing theworkpiece with a pusher.

However, in a conventional carburizing and quenching treatmentapparatus, a mounting position of the workpiece may shift from theintended mounting position when the workpiece is mounted on the mountingtable. In this case, during a heating process of the workpiece, thedistance between the periphery of the workpiece and a heat source (e.g.,induction heating coil) become nonuniform so that the workpiece cannotuniformly be heated. Further, during cooling of the workpiece in thequenching treatment, the workpiece cannot uniformly be cooled because ofthe shift in the position. Therefore, the carburizing and quenchingtreatment for the workpiece might not uniformly be carried out.Recently, it has become apparent that when the temperature change in theworkpiece is not uniform, a large heat treatment strain is produced,which results in failure to satisfy dimensional accuracy required forthe workpiece.

The mounted state of the workpiece during transportation also have aneffect on the heat treatment strain. Regarding the transportation andmounting of the workpiece, when a contact area between a transportmechanism or a mounting table and the workpiece is large, thetemperature change in the contact portion differs from the other portionof the workpiece, which might cause a large heat treatment strainresulting in failure to satisfy a dimensional accuracy required for theworkpiece.

For example, in a carburizing and quenching treatment apparatus of theonline-machining-production-system described in Japanese PatentApplication Laid-Open No. H10-53809, the mounting position of theworkpiece might shift from an intended position by tilting, vibration,or the like of a transportation fork. Further, since the treatment iscarried out without placing the workpiece in a tray, the mountingposition of the workpiece might shift from a suitable position whenworkpieces of different diameters are transported. Further, since acontact area between the workpiece and the transportation fork or acontact area between the workpiece and a mounting table is large andpartial, temperature change (temperature distribution) in a workpiecewill not be uniform. Therefore, the degree of thermal expansion andcontraction in a workpiece varies which produces heat treatment strainto cause deformation of the workpiece. This might result in failure tokeep the dimensional accuracy within a predetermined range aftercarburizing and quenching. Further, when one workpiece is transported ata time by a fork as described in Japanese Patent Application Laid-OpenNo. H10-53809 (or transported by a pusher as will be described below),the workpiece might slide on the fork or the like to be damaged.

Further, in carburizing and quenching treatment apparatuses described inJapanese Patent Application Laid-Open No. 2010-266176 and JapanesePatent Application Laid-Open No. 2003-183728 workpieces are transportedby a transportation fork on a tray, and the mounting position of theworkpiece might shift from a suitable position by, for example, tiltingof the transportation fork. Further, in the carburizing and quenchingtreatment apparatus described in Japanese Patent Application Laid-OpenNo. H8-285462, a tray is transported by a pusher, and shifting from asuitable position might occur due to variation in, for example, a pushstroke of a pusher

Further, as described in Japanese Patent Application Laid-Open No.2010-266176, Japanese Patent Application Laid-Open No. 2003-183728, andJapanese Patent Application Laid-Open No. H8-285462, a method ofcarrying out carburizing and quenching treatment for a plurality ofworkpieces in a tray is conventionally used. In such method, naturally,the temperature differs for each location in which each workpiece isplaced in the tray, and therefore, the temperature is controlled withina predetermined range of temperature distribution. However, in recentyears, some workpieces require particularly strict dimensional accuracyafter carburizing and quenching. It has become apparent that for suchworkpieces, it is difficult to satisfy the requirement by the method ofcarrying out carburizing and quenching treatment for a plurality ofworkpieces in a tray.

SUMMARY OF THE INVENTION

To solve the problem mentioned above, the object of the presentinvention is to provide a heat treatment apparatus which can mount aworkpiece in a suitable position on a mounting table as well as reducethe contact area between the workpiece and other parts during atreatment process, that is, to provide a heat treatment apparatus whichcan carry out carburizing and quenching treatment providing highdimensional accuracy of a workpiece after carburizing and quenching.

To achieve the object, the present invention provides a heat treatmentapparatus for carrying out carburizing treatment and/or quenchingtreatment for a circular workpiece including a treatment room configuredto carry out a predetermined treatment for a workpiece, a transportationmechanism configured to transport the workpiece into the treatment roomor out of the treatment room, and a mounting table, provided inside thetreatment room, on which the workpiece transported into the treatmentroom is mounted. The feature of the heat treatment apparatus is that thetransportation mechanism includes a transportation arm which mounts andmoves the workpiece, at least three transport support pins which supportthe workpiece during transportation are provided on the transportationarm, and at least three mounting table support pins which support theworkpiece are provided on the mounting table.

According to the present invention, the workpiece can be mounted on asuitable position on the mounting table when carburizing treatmentand/or quenching treatment is carried out for the workpiece. Further,the contact area between the workpiece and other parts can be reduced.In this manner, uniform temperature change in the workpiece can beprovided, thereby allowing uniform carburizing treatment and/orquenching treatment for the workpiece to be carried out as well asrestraining heat treatment strain produced in the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal cross sectional view of a heat(carburizing) treatment apparatus according to an embodiment of thepresent invention;

FIG. 2 is a cross sectional view taken along the line A-A in FIG. 1 (topview of a mounting table and a transportation arm when the figure is cutat A-A line);

FIG. 3 is a figure illustrating a configuration of a supporting aworkpiece formed of a circular top portion and a cylindrical sideportion;

FIG. 4 is a longitudinal cross sectional view taken along the line B-Bin FIG. 3;

FIG. 5 is a figure illustrating a heat (carburizing) treatment processaccording to an embodiment of the present invention;

FIG. 6 is a figure illustrating a heat (carburizing) treatment processaccording to an embodiment of the present invention;

FIG. 7 is a figure illustrating a heat (carburizing) treatment processaccording to an embodiment of the present invention;

FIG. 8 is a figure illustrating a heat (carburizing) treatment processaccording to an embodiment of the present invention;

FIG. 9 is a figure illustrating a heat (carburizing) treatment processaccording to an embodiment of the present invention;

FIG. 10 is an enlarged view of FIG. 8; and

FIG. 11 is a longitudinal cross sectional view taken along the line B-Bin FIG. 3 according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described based on a heattreatment apparatus 1 for carrying out vacuum carburizing and quenchingtreatment for a circular workpiece W below. Note that, the circularworkpiece indicates a workpiece having a column shape or a ring shape,or a workpiece formed of a circular top portion and a cylindrical sideportion, that is, a workpiece having a circular shape such as a lid, atray, and a bowl. Specifically, a mechanical part such as a gear is anobject to be treated. Further, in the specification and the drawings, acomponent having essentially the same functional configuration isappended with the same reference sign to omit repeated description.

As illustrated in FIG. 1, the heat treatment apparatus 1 includes avacuum sealable treatment room 2 for carrying out a predeterminedtreatment for a workpiece, a transportation mechanism 3 for transportingthe workpiece W into the treatment room or out of the treatment room,and a mounting table 4 on which the workpiece W transported into thetreatment room is mounted. Note that, the predetermined treatment is aprocess such as preheating, carburizing, diffusion, cooling, andquenching (including gas quenching), required in a conventional vacuumcarburizing treatment.

A driving device 5 is arranged in the lower part of the treatment room2. The driving device 5 is provided with a drive arm 6 extending upwardfrom the driving device 5. The distal end of the drive arm 6 penetratesthe bottom of the treatment room 2 to be connected to the mounting table4. The drive arm 6 functions as a strut of the mounting table 4. Sincethe driving device 5 is configured to allow the drive arm 6 to ascendand descend, the mounting table 4 can move to ascend and descendtogether with the drive arm 6.

As illustrated in FIG. 2, the mounting table 4 is configured with threeprotruding portions 8 (hereinafter referred to as “support fan 8”)provided so as to radially protrude from the center 7 (distal end of thedrive arm 6 illustrated in FIG. 1) of the mounting table 4 in a planview (top view). The angle between neighboring support fans 8 is thesame. A mounting table support pin 9 for supporting the workpiece W isprovided on the distal end of each support fan 8. The workpiece W istransferred to the mounting table support pin 9 from the transportationarm 10, which will be described below, and thereby the workpiece W issupported on the mounting table 4 by a three-point support. Note that,as a material of each support fan 8 and the mounting table support pin9, SUS304 or the like is used. Further, in FIG. 2, only the outer edgeof the workpiece W is illustrated in a dashed line.

Note that, as illustrated in FIG. 3 and FIG. 4, when the workpiece W hasa shape formed of, for example, a circular top portion W1 and acylindrical side portion W2, that is, for a workpiece having a hollowbottomed shape like a circular tray facing downward, such as a gear, theworkpiece W can also be supported by arranging three mounting tablesupport pins 9 on the mounting table 4 so as to contact the top portionW1 of the workpiece W in the inner side of the hollow portion of theworkpiece W. In this case, the mounting table support pin 9 ispreferably configured that the inner diameter of the side portion W2 ofthe workpiece W and the diameter of a circle (an imaginary circle)determined so as distal ends of three mounting table support pins 9 tobe on the circle are approximately the same. The mounting table supportpin 9 having such relationship between the workpiece W can also providea function of positioning of the workpiece W.

As illustrated in FIG. 1, the transportation mechanism 3 is configuredwith the transportation arm 10 which mounts and transports the workpieceW and a transportation device, not shown in the drawing, forhorizontally moving the transportation arm 10. As illustrated in FIG. 2,the distal ends of the transportation arm 10 form in a trifurcated shapeand these distal ends are provided to protrude toward the center 7 ofthe mounting table 4 (protruding portion 11). Each protruding portion 11is arranged so as to be able to support the workpiece W between supportfans 8 when viewed in a plan view. The angle between neighboringprotruding portions 11 is the same. Near the distal end of eachprotruding portion 11, a transport support pin 12 which supports theworkpiece W during transportation of the workpiece W is provided. Theworkpiece W is supported by the transport support pin 12 with athree-point support.

Note that, as illustrated in FIG. 3 and FIG. 4, when the workpiece W hasa shape formed of, for example, a circular top portion W1 and acylindrical side portion W2, that is, for a workpiece having a hollowbottomed shape like a circular tray facing downward, such as a gear, theworkpiece W can also be supported by arranging three transport supportpins 12 on the transportation arm 10 so as to contact the top portion W1of the workpiece W in the inner side of the hollow portion of theworkpiece W. In this case, the transport support pin 12 is preferablyconfigured that the inner diameter of the side portion W2 of theworkpiece W and the diameter of a circle (an imaginary circle)determined so as distal ends of three transport support pins 12 to be onthe circle are approximately the same. The relationship between theworkpiece W and the transport support pin 12 can provide positioning ofthe workpiece W by moving the transportation arm 10 so as to allow thetransport support pin 12 to contact and support the top portion W1 ofthe workpiece W in the inner side of the hollow portion of the workpieceW. That is, the transport support pin 12 also provides a function ofpositioning.

Further, in the embodiment, as illustrated in FIG. 1 and FIG. 2, anassist pin 13 is provided in the periphery of each transport support pin12. The assist pin 13 prevents falling of the workpiece W or determinesthe mounting position against the transport support pin 12 when theworkpiece W is mounted on the transport support pin 12. Each assist pin13 is arranged in a location so as to face the side surface of theworkpiece W when the workpiece W is mounted on the transport support pin12. Further, a portion of the side, facing the side surface of theworkpiece W, of each assist pin 13 is formed in a tapered shape whichbecomes thinner toward the top end of the assist pin 13 (tapered portion13 a).

For example, in a case, when the workpiece W does not have a circularshape having a hollow portion as described above, the workpiece whichhappens not to be in the suitable mounting position when being mountedon the transport support pin 12 moves along the tapered portion 13 a ofeach assist pin 13 to be correctly positioned. In this manner, when theworkpiece W is transferred between the mounting table 4 and thetransportation arm 10, the mounting position of the workpiece W againstthe transport support pin 12 is always the same. Further, at a point oftime when the workpiece W is mounted on the transport support pin 12,shifting of the position or falling of the workpiece W is restricted byeach assist pin 13 facing (or making contact with) the side surface ofthe workpiece W. Therefore, during transportation of the workpiece W,shifting of the mounting position against the transport support pin 12or falling of the workpiece W will not occur. Note that, as a materialof the transport support pin 12 and the assist pin 13, SUS304 or thelike is used.

Further, each mounting table support pin 9 and each transport supportpin 12 are preferably provided so as to be arranged on the samecircumference in a plan view when the workpiece W is mounted on themounting table 4. In this manner, tilting or such of the workpiece, whentransferring the workpiece W to the mounting table 4 from thetransportation arm 10, can be reduced, thereby restraining shifting ofthe workpiece W from the suitable mounting position.

Further, as illustrated in FIG. 1, the treatment room 2 is provided withan aperture 14 allowing transporting the workpiece W into and out of thetreatment room 2. Further, an open/close door 15 which seals thetreatment room 2 by closing the aperture 14 is provided adjacent to thetreatment room 2. The open/close door 15 is configured to be able tomove upward and downward by an open/close mechanism not shown in thedrawing. Further, an induction heating coil 16 which heats the workpieceduring carburizing is provided above the mounting table 4 inside thetreatment room. Note that, the heat treatment apparatus 1 according tothe embodiment includes other configurations necessary for carrying outa conventional vacuum carburizing such as an exhaust mechanism and acarburizing gas introducing mechanism though not shown in the drawing.

A carburizing method using the heat treatment apparatus 1 configured asdescribed above will be described.

First, as illustrated in FIG. 5, a workpiece W, which a preheatingtreatment according to the previous process of the carburizing treatmentprocess is completed, is transported, mounted on the transportation arm10, into the evacuated treatment room 2.

The workpiece W is transferred to the transport support pin 12 of thetransportation arm 10 from a mounting table (not shown in the drawing)of the treatment room of the previous process. Further, since eachassist pin 13 faces the side surface of the workpiece W, shifting of themounting position against the transport support pin 12 or falling of theworkpiece W during transportation of the workpiece W will not occur.Further, the transportation arm 10 extending into the treatment room iscontrolled so as to extend to be in a location in which the distancebetween the periphery of the workpiece W mounted on the mounting table 4and the induction heating coil 16 is uniform when the mounting table 4is in the ascended position as described below. That is, the workpiece Wtransported into the treatment room 2 is supported at a location inwhich the distance between the periphery of the workpiece W and theinduction heating coil 16 is uniform in a plan view.

Note that, as illustrated in FIG. 3 and FIG. 4, when the workpiece Whas, for example, a hollow bottomed shape like a circular tray facingdownward, such as a gear, the workpiece W can also be positioned byarranging three transport support pins 12 on the transportation arm 10so as to contact the top portion W1 in the inner side of the hollowportion and to contact (or to be located very close to) the side portionW2. That is, when the workpiece W has a shape formed of the circular topportion W1 and the cylindrical side portion W2, and when the transportsupport pin 12 is arranged on the protruding portion 11 so as to be on acircumference having an approximately the same diameter as the innerdiameter of the side portion W2 of the workpiece W, the transportsupport pin 12 can also provide a function of positioning.

Now, as illustrated in FIG. 6, the mounting table 4 ascends by the drivearm 6 made to ascend by the driving device 5. Then the workpiece Wsupported on the transport support pin 12 is transferred to the mountingtable support pin 9 provided on the mounting table 4. In this step, themovement of the mounting table 4 is only ascending and descending, sothat the mounting position of the workpiece W will not shift from thesuitable position. Then, the mounting table 4 ascends to the locationwhere the induction heating coil 16 is provided.

In this case, as illustrated in FIG. 3 and FIG. 4, when the workpiece Whas a hollow bottomed shape like a circular tray facing downward, suchas a gear, the workpiece W can also be positioned by arranging threemounting table support pins 9 on the mounting table 4 so as to contactthe top portion W1 in the inner side of the hollow portion and tocontact (or to be located very close to) the side portion W2. That is,when the workpiece W has the shape formed of the circular top portion W1and the cylindrical side portion W2, and when the mounting table supportpin 9 is arranged on the mounting table 4 so as to be on a circumferencehaving an approximately the same diameter as the inner diameter of theside portion W2 of the workpiece W, the mounting table support pin 9 canalso provide a function of positioning.

Then, as illustrated in FIG. 7, the transportation arm 10 moves outsidethe treatment room, and the open/close door 15 is closed to seal thetreatment room 2. Then, carburizing gas is introduced into the treatmentroom by the carburizing gas introducing mechanism not shown in thedrawing. Then, a high-frequency current is supplied to the inductionheating coil 16 to heat the workpiece W to the carburizing temperature.Since the workpiece W is supported by a three-point support of themounting table support pin 9, the contact area between the workpiece Wand the mounting table support pin 9 is small. The distal end portion ofthe mounting table 9 is provided with an arc shape of, for example, R1to R2 so as to prevent damaging to the workpiece W. However, the contactcan be assumed as a point contact. Therefore, the effect of the mountingtable support pin 9 is negligible and the workpiece W can uniformly beheated. Further, since the workpiece W is mounted in a location in whichthe distance between the periphery of the workpiece W and the inductionheating coil 16 is uniform, the workpiece W can uniformly be heated.Note that, the carburizing treatment temperature is approximately 850°C. to 1100° C. Further, when the workpiece W having an approximatelycircular shape such as a gear is heated by the induction heatingmentioned above, a concentric temperature distribution from the centerof the circle to the outer region is produced. The temperaturedistribution having a same temperature at locations of which distancesfrom the center of the circle are the same is preferable. The presentinvention can provide such temperature distribution so that gooddimensional accuracy can be obtained.

After carburizing treatment is complete, the carburizing gas isexhausted by the exhaust mechanism not shown in the drawing and thetreatment room is vacuumed.

Next, the open/close door 15 ascends and the transportation arm 10 movesinto the treatment room. Then, as illustrated in FIG. 8, the mountingtable 4 descends to transfer the workpiece W mounted on the mountingtable support pin 9 of the mounting table 4 to the transport support pin12 of the transportation arm 10. In this step, when the location of theworkpiece W is not in a suitable mounting position, as illustrated inFIG. 10, the workpiece W moves along the tapered portion 13 a of theassist pin 13 in the direction shown in the arrow in FIG. 10 to bemounted on the transport support pin 12. In this manner, even after thecarburizing treatment, the workpiece can always be mounted in the samemounting position against the transport support pin 12. Therefore, evenwhen the workpiece W is mounted on the mounting table (not shown in thedrawing) in the treatment room for cooling process which is the afterprocess, the workpiece W can be mounted in the suitable position, sothat the workpiece W can uniformly be cooled.

Note that, when the workpiece W has the shape formed of the circular topportion W1 and the cylindrical side portion W2, and when the mountingtable support pin 9 and the transport support pin 12 are arranged on themounting table 4 and the transportation arm 10 so as to be on acircumference having an approximately the same diameter as the innerdiameter of the side portion W2 of the workpiece W, the mounting tablesupport pin 9 and the transport support pin 12 can also preferablyprovide a function of positioning or preventing falling of the workpieceW also in the treatment process such as carburizing treatment andquenching treatment.

Finally, as illustrated in FIG. 9, the transportation arm 10 on whichthe workpiece W is mounted moves outside the treatment room and thecarburizing treatment process completes.

As described above, according to the present invention, the contact areabetween the mounting table and the workpiece as well as the contact areabetween the transportation arm and the workpiece can be reduced sincethe workpiece is supported by a three-point support by the mountingtable and the transport support pin. In addition, the mounting tablesupport pin and the transport support pin can provide a function ofpositioning of the workpiece. Therefore, falling of the workpiece can beprevented, and the workpiece can be mounted in the mounting positionwhere the workpiece can uniformly be heated and cooled. Thereby, uniformtemperature change of the workpiece can be provided when the workpieceis heated or cooled. As a result, the heat treatment strain in theworkpiece is restrained and at the same time, uniform carburizingtreatment can be provided.

Further, as described in the embodiment of the present invention, whenthe assist pin having a tapered portion is provided on thetransportation arm, the workpiece which happens not to be in thesuitable mounting position when being mounted on the transport supportpin can move along the tapered portion of each assist pin, and thereby,the workpiece can be mounted in the suitable position. In this manner,uniform temperature change of the workpiece can be provided when theworkpiece is heated or cooled, and thereby, the heat treatment strain inthe workpiece is restrained and at the same time, uniform carburizingtreatment can be provided.

The preferable embodiment of the present invention is described above.However, the present invention is not limited to such example. It isapparent that those skilled in the art can make various alterations ormodifications within the scope of the technical idea described in theclaims, which naturally fall within a scope of the art of the presentinvention.

For example, in the embodiment, the assist pin is provided on thetransportation arm, though the assist pin can be provided on themounting table instead of the transportation arm. In this case, when theworkpiece is transferred from the transportation arm to the mountingtable, the workpiece moves along the tapered portion of the mountingtable support pin provided on the mounting table so as to be mounted onthe mounting table support pin. In this manner an effect similar to theeffect as described in the embodiment can be obtained. Further, when theassist pin is provided on both the mounting table and the transportationarm, the effect of preventing the shifting of the mounting position ofthe workpiece can further be improved.

Further, in the embodiment, a portion of the side, facing the sidesurface of the workpiece, of the assist pin is formed in a taperedshape, though all sides of the assist pin may be formed in a taperedshape. Further, the number and arrangement of the mounting table supportpin and the transport support pin are suitably changed according to theshape and size of the workpiece. That is, as long as the workpiece canbe supported without tilting when mounted on each support pin, anynumber and any arrangement may be provided. Similarly, the number of thesupport fan of the mounting table and the angle between each support fanas well as the number of the protruding portion of the transportationarm and the angle between each protruding portion may suitably bechanged.

Further, in the embodiment, the mounting table ascends to transfer theworkpiece between the mounting table and the transportation arm.However, an ascend-and-descend mechanism may be provided to thetransportation mechanism to make the transportation arm ascend anddescend. In this case, the workpiece can be mounted on the mountingtable without ascending or descending the mounting table. Further, arotation mechanism can be provided to the driving device which makes themounting table ascend and descend. In this case, the mounting table canbe rotated during the heating and cooling of the workpiece, so that theworkpiece can further uniformly be heated and cooled.

Further, in the embodiment, the vacuum carburizing treatment apparatusis used as an example of a heat treatment apparatus in the description,though it is not limited to the vacuum carburizing treatment apparatus,and other treatment apparatus may be used. Similarly, in other processesin the carburizing treatment, that is, a preheating process, a diffusionprocess, and a cooling (soaking) process, the heat treatment apparatusof the present invention can be used.

Further, the heat treatment apparatus according to the present inventioncan be applied for quenching treatment. For example, when the quenchingtreatment by gas cooling is carried out, instead of using a coil forinduction heating, a cooling device configured to blow a cooling gas,uniformly in a plan view, to the outer circumference of the circularworkpiece W is preferably used to carry out quenching (cooling) keepinguniformity of the temperature during cooling.

Further, in the present invention, it is preferable to carry outtreatment for one workpiece at a time to obtain a workpiece havingexcellent dimensional accuracy. However, if geometric symmetry withreference to a heat source or a cooing source can be maintained duringtemperature control of the workpiece, treatment can be carried out fortwo or more workpieces at a time.

Further, as illustrated in FIG. 11, a workpiece W having a certain formmay be heat treated on a tray. In this case, a tray T supporting theworkpiece W is supported by the transport support pin 12 of thetransportation arm, and transported into the treatment room by thetransportation arm. Then, the tray T transported into the treatment roomis transferred from the transport support pin 12 to the mounting tablesupport pin 9 by, for example, ascending and descending of the mountingtable. In this step, it is preferable to provide at least three traysupport pins 17 for supporting the workpiece W on the top surface of thetray T.

Further, for example, when a tray T having a shape formed of a circulartop portion T1 and a cylindrical side portion T2 is used, the mountingtable support pin 9 is preferably be arranged on the mounting table soas to be on a circumference having an approximately the same diameter asthe inner diameter of the side portion T2 of the tray T. Also by a heattreatment apparatus including such tray T, the effect as described inthe embodiment of the present invention can be obtained. Further, when atray T having the shape formed of the circular top portion T1 and thecylindrical side portion T2 is used, the transport support pin 12 may bearranged on the transportation arm so as to be on a circumference havingan approximately the same diameter as the inner diameter of the sideportion T2 of the tray T. Also by a heat treatment apparatus includingsuch tray T, the effect as described in the embodiment of the presentinvention can be obtained.

Furthermore, for example, when the workpiece W having a shape formed ofthe circular top portion W1 and the cylindrical side portion W2 issupported by a tray T, the tray support pin 17 is preferably be arrangedon the tray T so as to be on a circumference having an approximately thesame diameter as the inner diameter of the side portion W2 of theworkpiece W. A heat treatment apparatus including such tray T ispreferable in that the tray T can provide a function of positioning andthat the temperature variation in the workpiece W is restrained sincethe contact area between the tray T and the workpiece W is minimized.

What is claimed is:
 1. A heat treatment apparatus for carrying outcarburizing treatment and/or quenching treatment for a circularworkpiece comprising: a treatment room configured to carry out apredetermined treatment for the workpiece; a transportation mechanismconfigured to transport the workpiece into the treatment room and out ofthe treatment room; and a mounting table, provided in the treatmentroom, on which the workpiece transported into the treatment room ismounted, wherein the transportation mechanism includes a transportationarm which mounts and moves the workpiece, the transportation armprovided with at least three transport support pins which support theworkpiece when the workpiece is transported, and at least three mountingtable support pins which support the workpiece are provided on themounting table.
 2. The heat treatment apparatus according to claim 1,wherein the mounting table is configured with at least three supportfans each provided with the mounting table support pin, and each of thesupport fans is provided so as to radially protrude from a center of themounting table in a plan view.
 3. The heat treatment apparatus accordingto claim 1, wherein at least three protruding portions which protrudetoward a center of the mounting table and can support the workpiecebetween the support fans in a plan view are provided on a distal end ofthe transportation arm, and each of the protruding portions is providedwith the transport support pin which is arranged to support theworkpiece between the support fans in a plan view.
 4. The heat treatmentapparatus according to claim 1, further comprising an ascend-and-descendmechanism which makes the mounting table ascend and descend.
 5. The heattreatment apparatus according to claim 1, wherein the workpiece has ashape formed of a circular top portion and a cylindrical side portion,and the mounting table support pin is arranged on the mounting table soas to be on a circumference having an approximately a same diameter asan inner diameter of a side portion of the workpiece.
 6. The heattreatment apparatus according to claim 1, wherein the workpiece has ashape formed of a circular top portion and a cylindrical side portion,and the transport support pin is arranged on the transportation arm soas to be on a circumference having an approximately a same diameter asan inner diameter of a side portion of the workpiece.
 7. The heattreatment apparatus according to claim 1, further comprising a rotationmechanism which rotates the mounting table.
 8. The heat treatmentapparatus according to claim 1, wherein the mounting table support pinand the transport support pin are arranged on a same circumference whenthe workpiece is mounted on the mounting table.
 9. The heat treatmentapparatus according to claim 1, wherein the transportation arm includesan assist pin provided in a periphery of each transport support pin. 10.The heat treatment apparatus according to claim 9, wherein at least aportion of a side, facing a side surface of the workpiece, of the assistpin is formed in a tapered shape which becomes thinner toward a top endof the assist pin.
 11. The heat treatment apparatus according to claim1, further comprising a tray which supports the workpiece, wherein thetray supporting the workpiece is supported by the transport support pinand then transported by the transportation arm to be mounted on themounting table support pin, and at least three tray pins which supportthe workpiece are provided on a top surface of the tray.
 12. The heattreatment apparatus according to claim 11, wherein the tray has a shapeformed of a circular top portion and a cylindrical side portion, and themounting table support pin is arranged on the mounting table so as to beon a circumference having an approximately a same diameter as an innerdiameter of a side portion of the tray.
 13. The heat treatment apparatusaccording to claim 11, wherein the tray has a shape formed of a circulartop portion and a cylindrical side portion, and the transport supportpin is arranged on the transportation arm so as to be on a circumferencehaving an approximately a same diameter as an inner diameter of a sideportion of the tray.
 14. The heat treatment apparatus according to claim11, wherein the workpiece has a shape formed of a circular top portionand a cylindrical side portion, and the tray support pin is arranged onthe tray so as to be on a circumference having an approximately a samediameter as an inner diameter of a side portion of the workpiece.